Rotor head for a helicopter

ABSTRACT

This invention relates to a rotor head for a helicopter comprising a hollow rotor mast, ball end means mounted on the mast, spring rod means mounted in the mast, ball socket means having rotor blades secured thereto on one end of said spring rod means and the other end thereof being secured against rotation, and a longitudinally displaceable supporting means between the hollow mast and the spring rod means.

United States Patent Kannamuller et al.

[451 Jan. 25, 1972 ROTOR HEAD FOR A HELICOPTER [72] Inventors: Gerhard Kannamuller, Markdorf; Karll-lelnz Kosziech, Friedrichshafen; Werner Goller, Bermatingen; Walter Kugler; Yorck Muller, both of Friedrichshafen, all of Germany [73] Assignee: Dornier A.G., Friedrichshafen am Bodensie, Germany [22] Filed: Feb. 12, 1970 [21] App1.No.: 10,744

[30] Foreign Application Priority Data Feb. 26, 1969 Germany ..P 19 09 501.3

[52] U.S.Cl ..416/138,416/l02,416/l48 [51] Int. Cl ..B64c 27/52 [58] Field ofSearch ..416/102, 138, 148

[56] References Cited UNlTED STATES PATENTS 3,080,002 3/1963 Du Pont ..416/148 X 3,451,484

6/1969 Sawicki et al FOREIGN PATENTS OR APPLICATIONS 929,021 6/1947 France ..416/148 1,044,231 6/1953 France ..416/148 263,599 1/1927 Great Britain 608,459 9/1948 Great Britain ...4l6/l48 ...416/148 Great Britain 416/102 Primary Examiner-Everette A, Powell, Jr. Attorney-James E. Bryan 57 I ABSTRACT This invention relates to a rotor head for a helicopter comprising a hollow rotor mast, ball end means mounted on the mast, spring rod means mounted in the mast, ball socket means havin g rotor blades secured thereto on one end of said spring rod means and the other end thereof being secured against rotation, and a longitudinally displaceable supporting means between the hollow mast and the spring rod means.

3 Claims, 1 Drawing Figure PATENIEI] JAHZSIQYZ 3.637.322

INVENTORS GERHARD KANNAMULLER KARL- HEINZ KOSZIECH WERNER s'o'LLER WALTER 'KUGLER YORCK MULLER ROTOR HEAD FOR A HELICOPTER This invention relates to a rotor head for a helicopter, designed particularly for a shaft drive, in which the rotor blades are connected with the rotor mast in a semirigid construction. The head is mounted, by means of a ball end and ball socket, so as to be inclinable or tiltable in all directions at the upper end of the rotor mast, which latter is constructed as a hollow shaft. The rotor blades are secured to the ball socket.

Rotor blade connections in rigid or semirigid constructions are known to the art as well as rotor blade connections which are provided with flapping hinges. Both of these basically different types of blade connections, such as rigid and jointed rotor blade connections, have certain advantages, but also have a number of disadvantages.

One advantage of the rigid blade connection resides in the simplicity of construction, manufacture, and maintenance thereof, which is due to the elimination of flapping and of drag hinges. In addition to this simplification, a rotor system of this type in which the flapping hinges are eliminated also has advantages from a technological point of view. In a rotor having a central flapping hinge, i.e., by reason of a semirigid rotor system, moments can be transmitted to the airframe only by inclining the rotor, i.e., by the drift of the thrust resultant out of the center of gravity of the helicopter. As a consequence, the control effectiveness as well as the permissible center of gravity range are limited. An improvement of these properties is effected, for example, by means of flapping hinges which are positioned outside of the rotor center since, in such case an additional moment can be exerted upon the rotor head by the forces acting in the direction of the blade axis. The same effect, only considerably greater, is achieved with the aid of a hingeless blade connection. The pitch damping and the rolling damping increases in the same proportion as the control effectiveness so that the aerodynamic properties in hovering flight can be significantly improved.

A further advantage of the rigid rotor as compared to a rotor with flapping hinges is apparent at high-flying speeds. In such case, the rotor must be relieved with respect to thrust because of the irregularity of the airflow conditionsduring the blade rotation. With a jointed rotor, only small moments can be transmitted to the airframe in the course of an increasing relief by inclination of the thrust resultant, so that an additional control about the pitch and roll axis by means of elevators or ailerons is necessary. The rigid rotor, on the other hand, even when completely relieved still can supply all of the required control moments so that a single control, i.e., the cyclic blade control, can be utilized for all flying ranges.

In the case of a jointed or hinged blade connection, the greater harmonics of the flapping movements become progressively more apparent due to the nonuniformity of the airflow conditions at the rotor blade at higher speeds until flapping instability finally will occur. By means of the hingeless blade connection, the higher harmonics of the flapping movements are largely suppressed and, hence, the flapping instability limit is shifted toward higher advanced coefficients, i.e., towards higher flying speeds. The susceptibility to squalls and pitch angle sensitiveness, which increase with the forward speed. may be equalized by a blade angle return control, or a mechanical gyroscope, or an electronic stabilizing means. In the case of hingedly connected rotor blades, a phase shift of 90 will be produced during the cyclic control between the variation of the blade setting angle and the appearance of the corresponding control movement. In extremely rigid rotor blades and a hingeless blade connection, this phase shift or phase displacement becomes zero. For reasons pertaining to stresses and for stability reasons during high-speed flight, the blade suspension or the blades themselves in the hingeless rotor blades known to the art are constructed so flexibly that the phase angle is between 50 and 70. The phase displacement between the excitation and the response is taken into account with regard to the control kinematics so as to prevent coupling effects. Not susceptible to being influenced by the control kinematics are, on the other hand, coupling effects during the damping moments which, however, may be attenuated by a favorable selection of the blade mass constant.

, impact rigidity is desirable,

For takeoff and landing on a slope, the hinged rotor, for example, is superior since a large angle of inclination is possible between the rotor and the landing gear. In hovering flight and in slow-speed flight, the rigid rotor is superior because of its excellent stabilizing properties. For high-speed flight, a lower as compared to hovering flight, because of the susceptibility to squalls and dynamic instability. If it is desired to stop the rotor in flight, in the case of a convertiplane, a high impact rigidity isagain required.

The occurrence of considerable rotor and airframe stresses during landing on uneven terrain and on moving ship decks is one disadvantage of the high impact rigidity. A further disadvantage resides in the susceptibility to squalls and the pitch angle sensitiveness due to the high impact rigidity which, in turn, results at higher speed which, in turn, results that at higher speeds the rotor can produce very high loads and longitudinal pitching moments. The longitudinal pitching moment must be counteracted by means of an extremely large horizontal tail assembly or a gyroscopic stabilizing means. The squall loads, on the other hand, cannot be alleviated.

Accordingly, various requirements must be met in connection with an ideal rotor, particularly for compound helicopters which travel at high-flying speeds. The present invention provides a rotor head for a helicopter which combines the advantages of the hinged rotor blade suspension with the advantages of the rigid rotor blade suspension without, however, including the disadvantages thereof. In hovering flight, the rotor should display a high degree of tipping damping and control effectiveness without being pitch-angle-sensitive and susceptible to squalls during high-speed flight. Moreover, this rotor is suitable for use in extreme landing conditions without the appearance of undesirable coupling effects during the control and damping operations.

The present invention begins with a rotor head for helicopters, particularly for ashaft drive, having rotor blades connected with the rotor mast in a semirigid construction. The head is so mounted at the upper end of the rotor mast, by means of a ball end and ball socket, as to be inclinable or tiltable in all directions; the rotorblades are secured to the ball socket. In the construction of the present invention, the rotor mast carrying the ball end is constructed as a hollow shaft and a spring rod is guided therein carrying the ball socket on one end thereof with the other end thereof being clamped in so as to be rigid against torsion or rotation. A supporting element is longitudinally displaceably mounted between the hollow shaft and the spring rod, which ensures that the spring rigidity of the spring rod can be varied. In order that it be possible to effect a simple displacement, the supporting element can be constructed as a slide sleeve which is displaceable by the pilot as may be desired. Thus, a variable rotor blade suspension is actually obtained, i.e., a variable impact rigidity which acts like a rigid and/or a hinged rotor blade suspension, and the advantages of which may be utilized in each case by the pilot.

In addition to the advantages which are afforded with respect to the aerodynamic properties, the desirable effect of thevariable impact rigidity upon the rotor stress also should be noted. By virtue of a favorable adaption or coordination of the impact rigidity and pivot rigidity, it is possible to greatly reduce the stress of the blades in any flight phase. As a result, the service life of the blades can be considerably extended.

The invention will be further illustrated by reference to the accompanying drawing which shows a rotor head according to the present invention in a cross-sectional view.

As is apparent from the drawing, the rotor head includes the rotor mast 1 and the ball end 2 mounted at the upper end of the rotor mast l. The ball socket 3 coordinated to the ball end 2 contains the connections 4 for the rotor blades 5. The rotor mast l is constructed as a hollow shaft and transmits the flux of force from the driving engine. Installed at the interior of the ball end 2, which is constructed as a hollow body and, respectively, of the ball socket 3, is a synchronizing hinge6 which transmits the torsional moment or propeller torque in any angular position during flapping movements of the rotor blades. Also mounted in the ball socket 3 are the bearings 7 in which the upper end of the spring rod 8 is mounted. The spring rod 8 is received within the rotor mast l and the other end thereof is secured against torsion or rotation with the airframe 11. Inserted in the rotor mast 1 between the hollow shaft and the spring rod 8 is a supporting element 9 which is constructed as a slide sleeve. By means of the linkages 10, the slide sleeve may be axially displaced in the hollow shaft, as indicated by the arrow A. The supporting element 9, i.e., the slide sleeve, is movably connected with the spring rod 8 by means of a spherical bearing 12. This has the purpose of compensating for any unevenness in the position of the spring rod 8.

It is also apparent from the drawing that the rotor head, which is mounted at the ball end 2 by means of the ball socket 3, is so mounted as to be movable in all directions. This setting or positioning of the rotor head corresponds, with respect to the function thereof, approximately to the conventional semirigid construction. By virtue of the fact that the spring rod 8 extends from the ball socket 3 within the rotor mast 1 toward a torsion-rigid clamping point on the airframe, the ball socket 3 is retained in a central position at all times. Depending upon the construction of the spring rod 8, the spring rigidity will have a specific value but, as has been noted above, ti is advantageous on the one hand that there be present a low spring rigidity and that, on the other hand, the rotor blade suspension possess a maximum rigidity. The spring rigidity may be adjusted as desired by means of an axial displacement of the slide sleeve. This means in actual fact that the slide sleeve fulfills the function of a supporting hearing when the spring rod 8 is considered as a unilaterally clamped-in carrier. When the slide sleeve is in the lowermost position thereof, the spring rod 8 may be strongly deflected due to the stress of the rotor hub. In order to prevent this strong deflection, it is sufficient to simply move the slide sleeve upwardly so that the deflection will be smaller. This assures that a helicopter having a rotor head according to the present invention combines in each case the advantages of the hinged rotor blade connection with those of the rigid blade connection without any disadvantages arising.

In the case of a variation or modification of the impact rigidity, the phase angle between the cyclic control deflection and the control moment will change as well, i.e., the coordination of the control stick movements and the control effect. In order not to unduly burden the pilot, this coordination should remain unchanged, with the aid of special provisions, in any possible rigidities of the rotor. One relatively simple possibility is afforded by a twisting of the airframe-side swash plate portion during a variation of the impact rigidity. Moreover, by increasing the rotational speed of the rotor, the phase angle may be maintained constant in the case of a varying spring rigidity. This possibility is suggested particularly in the case of reaction-propelled rotors in which, as is known, the rotational speed is independent of the speed of the driving engine.

The greatest rigidity is indicated in hovering flight for reasons of stability. In order that the phase angle be maintained constant, a maximum rotor speed is desired. The highrotational speed of the rotor represents a reserve margin of power in case of a propulsion unit malfunction. With increasing forward speed, the impact rigidity is reduced because of the pitch angle sensitivity. In high-speed flight, a reduction of the rotational speed is desirable because of the mach number effects on the rotating rotor blade. As a result of this measure, the phase angle remains constant. A further possibility of maintaining the phase angle constant when the impact rigidity varies is afforded by a favorable coordination or adaption of the mechanical blade angle return displacement or the additional flapping movement damping within the entire flight range.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is: l. A rotor head for a helicopter comprising a hollow rotor mast, ball end means mounted on the mast, spring rod means mounted in the mast, ball socket means having rotor blades secured thereto on one end of said spring rod means and the other end thereof being secured against rotation, and a longitudinally displaceable supporting means between the hollow mast and the spring rod means.

2. A rotor head according to claim 1 in which the supporting means is a slide sleeve having means connected thereto whereby it may be displaced by a pilot.

3. A rotor head according to claim 2 in which the slide sleeve contains a spherical bearing for guiding the spring rod means. 

1. A rotor head for a helicopter comprising a hollow rotor mast, ball end means mounted on the mast, spring rod means mounted in the mast, ball socket means having rotor blades secured thereto on one end of said spring rod means and the other end thereof being secured against rotation, and a longitudinally displaceable supporting means between the hollow mast and the spring rod means.
 2. A rotor head according to claim 1 in which the supporting means is a slide sleeve having means connected thereto whereby it may be displaced by a pilot.
 3. A rotor head according to claim 2 in which the slide sleeve contains a spherical bearing for guiding the spring rod means. 